[grey88gt]

I may be way off here but I think hes refering to pinging, or predetnation. Slow your timeing down, your igniting the fuel way to soon and your hearing the uncontroled combustion in the clyinder, thats why it got worse with mid grade fuel becuase it burns at a faster rate. I think 18deg timeing is insane. Iam suprized you havent cuased other problems in yout engine because of to much timeing. Buy the way dieseling is when an engine trys to keep running after you trun it off, also caused buy low grade fuel, to much timeing, ideling to fast, hot engine with very high compresion. and what Brcuda says.